1. Field of the Invention
The present invention relates to a lens-attached matter detector which detects attached matter on a lens of a camera, for example, a lens-attached matter detection method, and a vehicle system including the lens-attached matter detector.
2. Description of the Related Art
A system is known which detects a vehicle or a pedestrian existing in a blind area behind a vehicle by an in-vehicle camera when changing a lane, so as to draw a driver's attention by an alarm or an indication light. A system is also known which detects a white line on a road by a camera, so as to draw a driver's attention by an alarm or an indication light when a driver drifts from a lane. Further, a system which sounds a red alert by detecting a vehicle getting closer from behind and a system which assists parking by detecting a parking frame are also known. Hereinafter, an in-vehicle system using an image recognition technique is referred to as an image-sensing application.
A camera for use in such a system may be provided outside a vehicle, and is used while the vehicle is running. For this reason, a stain such as splash of dirt attaches onto a lens surface. When such a stain is prominent, the detection accuracy of a subject by a camera is deteriorated. For this reason, the performance of an image-sensing application such as a system which detects a vehicle or a pedestrian, or a system which detects a white line may be affected. Thus, when a driver is aware of a stain, such a stain is eliminated from a lens by spraying air or cleaning liquid.
However, a driver is sometimes not aware of a stain. For this reason, a stain detector, which automatically detects a stain on a lens, so as to encourage cleaning by informing a driver of the generation of the stain or automatically clean the stain, has been developed (refer to, for example, JP 2003-259358A). In the stain detector described in JP 2003-259358A, a concentration value is obtained for each of two images shot by a camera in different timings, and a difference of these values is extracted to be integrated, so as to obtain an integrated image. In such an integrated image, an area having a predetermined concentration value or below, namely, an area without having a change over time is determined as an area to which a stain is attached. When this stain-attached area is an area for use in an image process by a camera, it is determined that a lens is stained, and a stain-attached signal is sent to a driver or a cleaner.
However, in the stain detector described in JP 2003-259358A, a landscape or an object to be shot (for example, long guide rail, parapet, or side walk) having less change over time has an increased concentration value of an integrated image with a difference, causing false-determination as a stain. Therefore, the development of a highly accurate technique which can detect only attached matter on a lens such as a stain is requested.